1. Field of the Invention
The present invention relates to a peptide of virus for crustaceans, especially relates to a peptide of white spot syndrome virus (WSSV), which highly expressed in their hosts.
2. The Prior Arts
Aquaculture is an important industry in most of the Asian countries. However, it has been threatened by several virus-induced diseases recently because of high-density cultivation. White spot disease (WSD) is one of the major diseases causing tremendous economic losses in aquaculture industry. The most observed clinical sign of WSD is white spots in the exoskeleton in diseased shrimp, especially in the head region (cephalothorax). White spot syndrome virus (WSSV) is the causative pathogen of WSD, which can cause high infectivity and high mortality of infected shrimps. WSSV has a wide host range among crustaceans, included many species of cultured and wild shrimp, crab, crayfish, lobster. Crabs are reservoir hosts for the WSSV virus because of their tolerance. The cumulative mortality rate can reach 100% for the WSSV-infected shrimps within 2 to 10 days from the onset of gross visible signs. The high morbidity and high mortality qualities of WSD were received high attention for scientists and fisheries. WSD was first reported in a commercial shrimp production facility in Fu-Jian province of Mainland China in 1992, and subsequently found in many Asian countries including Taiwan, Korea, Thailand, Japan, India, the Philippines and Indonesia. For more than 10 years, WSD has been identified from Asia to the whole world, such as America. The damage has been made to all the shrimp production areas. Therefore, WSD is not only health threat to the crustaceans, but also results in devastating economic losses for aquaculture farmers.
To prevent and control WSD disease, global hatchery managers have to monitor the progress of the disease and detect the infection of WSSV in the aquaculture crustaceans during cultivation regularly. Nested Polymerase Chain Reaction (nested PCR) is a sensitive and specific diagnostic too and now commercially available for many viruses of aquaculture crustaceans, including WSSV.
Nested PCR uses two sets of amplification primers. The first pair of primer amplified a larger PCR product. Then a second PCR reaction is run with the second pair of primers using the product of the first reaction as the amplification target. This procedure increases the sensitivity of the assay, which is suitable for detection of low template concentration. Therefore it can be applied in analysis of trace quantities of DNA. However, nested PCR diagnostic kits are routinely used in research laboratories, the associated costs and the technical expertise required have prevented their widespread adoption in traditional aquaculture farmers.
Therefore, it would be helpful to develop a diagnostic test that was not only highly sensitive and rapid, but also cheap and easily performed. An immuno-based detection system is suggested for such a test. This test used a specific protein of virus as the detection target. Higher expression levels of target protein lead this immunodetection test more sensitive, even when viral titers are low in the hosts. Hence, target protein is the key element for the immunodetection technique. The expression of WSSV envelope protein VP28 is known to be the target protein for immunodetection. VP28 is regarded as the most highly expressed protein in WSSV in the past, but the expression level of VP28 is far beyond that of host proteins. Practically the application of VP28 in WSSV detection for crustaceans is limited by the amount unless being seriously infected.